| According to daily grid precipitation data, a generalized Meiyu criteria has beendefined in Yangtze-Huaihe region (28～34°N, 110～122°E). And the updated criteriaare applied to analyze the precipitation characteristics during the Meiyu period.What's more, the abnormal variability of summer climate in China during 1991～2005is simulated by means of BCC_RegCM1.0 (RegCM for short). Then according to theabove simulating results, the timing of onset and ending is defined and theperformance on simulating Meiyu in Yangtze-Huaihe region is analyzed for the recent15a. Furthermore, we discuss the effect of the initial value of spring soil moisture onthe following summer climate with the observation data and the simulated results,respectively. In the end, by using of the Newtonian Nudging method, we carry out theassimilation and the influence experiments on the initial filed of soil moisture.To summarize, the main results of this study are as follows:(1) By means of Cressman's objective analysis method, a 0.5°×0.5°grid pointdaily precipitation dataset of China for 1954～2005 has been obtained. Then, ageneralized Meiyu criterion has been define to investigate the Meiyu precipitationfeatures over the whole Yangtze-Huaihe region, including the Yangtze River and theHuaihe Basin Region. The updated criterion is applied to analyze the precipitationcharacteristics during the Meiyu period in the Yangtze-Huaihe region. Using RotatedEmpirical Orthogonal Function (REOF), there are four kind Meiyu precipitationpatterns in different regions, including the Yangtze-Huaihe region, the south of theYangtze River, the Huaihe River, as well as the Dongting Lake and the Poyang Lakevalley. The research is found that the Meiyu pattern in the south of the Yangtze Riveris decreasing, while the pattern in the Huaihe River is increasing.(2) The Meiyu parameters have an about 2～3a, 6～8a, 12～15a and 18～20adominating periods. The approximate 2～3a significant period of Meiyu parametersmay reflect the effects of Tropospheric Quasi-Biennial Oscillation (TBO). Threeobvious abrupt climatic changes have happened in the mid of 1960's, the late 1970'sthrough early 1980's and the early 1990's.(3) By using RegCM, the summer climatologic characters over China during1991～2005 are simulated. The research shows RegCM can simulate East-Asian meancirculation field. What's more, the simulated magnitude and spatial distribution ofsurface temperature is good agreement with observation. But the results show thebetter performance in the East China than in the West China. At the same time,RegCM can basically reproduce the spatial distribution of summer precipitation.Regardless of the spurious precipitation in Southwest region and Tibet Plateau, the departure between the observations and the simulated results vary within the range of2.6～73% in other regions. As for the march of the major seasonal rain belts, thoughbeing some deficiency for the pre-summer flood season to some extent in South China,there are better performances for the march towards the North of major rain belts afterJune, particularly for the simulation of Meiyu precipitation. Further, RegCM canbetter simulate the variables of the spatial distribution of land surface process insummer China.(4) RegCM is of the ability to simulate the inter-annual change ofYangtze-Huaihe Meiyu with preferable capability for most of the normal Meiyu years,especially for the strong Meiyu year of 1996a, 1998a and 1999a. In term of averagestatus for recent 15a Meiyu simulation, the timings of onset and ending occur earlier,Meiyu duration does 3-days earlier and Meiyu intensity index is weaker comparingwith the outcome defined by the observations.(5) With observation analyses, we can obtain that the surface (root) zone soilmoisture on spring in Yangtze-Huaihe River region is inversely (directly) proportionalto the surface temperature in the following summer. However, both the surface androot zone soil moisture on spring vary in the direct ratio of the summer precipitationin Yangtze-Huaihe River region.At the same time, the sensitivity experiments about the effect of the soil moistureon China climate are carrying out. Results show that:①As for the surfacetemperature, the double (halving) experiments of soil moisture initial value on April1st in different levels make the surface temperature reduce (increase) in followingsummer without exception.②For precipitation, the soil moisture of total (root) andsurface zone has an higher effect on the summer rainfall under the control of weak(strong) monsoon. Both the double and halving experiments will strengthen theprecipitation in most East China under the influence of strong monsoon, while theprecipitation caused by the halving experiment are much more than the equivalent bythe double test in the aspect of region range and magnitude.(6) Introducing the Newtonian nudging assimilation method with GSWP2 soilmoisture data in RegCM, we can distinctly improve the simulation of surfacetemperature in China and precipitation in Yangtze-Huaihe region under the influenceof the strong summer monsoon while inconspicuous improvement for the weaksummer monsoon years.
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